Hi,
If your 6-month-old Flowerhorn has not eaten anything for nearly a month, even though it is still active and your water parameters (pH, temperature, and regular water changes) are good, this is not normal and needs further investigation.
The fact that the fish takes the pellet into its mouth and spits it out often suggests one of the following:

• Internal bacterial or parasitic infection.
• Mouth or throat injury.
• Intestinal parasites.
• Poor-quality or stale food.
• Stress from unseen factors (tank mates, electrical leakage, etc.).

Here’s what I recommend:

1. Check the fish’s mouth carefully for any swelling, injury, fungus, or obstruction.
2. Try offering a different food such as frozen bloodworms, frozen shrimp, or high-quality cichlid pellets to see if the fish accepts them.
3. Observe the fish’s feces:
   • Long white/stringy feces often indicate internal parasites or a bacterial infection.
4. If internal parasites are suspected, use an appropriate anti-parasitic medication as per the manufacturer’s instructions.
5. If there are no signs of parasites but the condition continues, consider treating with a broad-spectrum antibacterial medication.
6. Continue maintaining excellent water quality and avoid overfeeding.

To help identify the exact cause, please share:

• A clear photo or short video of the fish.
• Is the fish passing white/stringy feces?
• Is the abdomen swollen or sunken?
• Which brand of pellets are you feeding?
• Is the fish kept alone or with other fish?

A Flowerhorn can survive for some time without food, but one month without eating is a serious concern. With a photo and answers to the above questions, I can suggest a more targeted treatment.
Regards,
Yashwant Naik